1. Field of the Invention
The present invention relates to a medical image processing apparatus, ultrasound imaging apparatus and X-ray CT apparatus, which generate image data suitable for diagnosis of a heart, and also relates to a method of processing a medical image.
2. Description of the Related Art
One of the important tasks in clinical diagnosis of a heart is advancement of a technique of assessing myocardial ischemia. In assessment of myocardial ischemia, an ultrasound imaging apparatus is used to capture an image by a method such as the color Doppler method and the contrast image method using a contrast medium. In this image capture, a state that the coronary artery or myocardium of the heart is deeply stained with the contrast medium is extracted as an ultrasound image such as a color Doppler image, a power Doppler image and a contrast image. Then, an ischemic part of the heart, which is a three-dimensional structure, is diagnosed by the extracted image.
An ultrasound imaging apparatus that is capable of acquiring volume data representing a three-dimensional region by scanning the inside of the three-dimensional region with ultrasound waves is known. By a three-dimensional ultrasound image such as a CFM (Color Flow Mapping) image, a power Doppler image and a three-dimensional contrast image generated by the ultrasound imaging apparatus, clinical diagnosis is conducted.
Further, an X-ray CT apparatus is provided with a multi detector and is thereby capable of generating image data of movement of a heart in real time. This enables observation of the movement of the heart as a three-dimensional moving image.
An ultrasound imaging apparatus for assessing myocardial ischemia by a three-dimensional image is known (e.g., Japanese Unexamined Patent Publication JP-A 2000-210289). This ultrasound imaging apparatus acquires volume data representing a heart by transmitting and receiving ultrasound waves. Then, the ultrasound imaging apparatus specifies a cardiac cavity region from the volume data and executes a mask process on data representing the inside of the cardiac cavity region. Then, the ultrasound imaging apparatus sets a division plane passing through the long axis of the heart, and divides, by the division plane, a region represented in the volume data subjected to the mask process into plural regions. By executing image processing such as the MIP (Maximum Intensity Projection) process on the divided volume data, the ultrasound imaging apparatus generates ultrasound image data such as MIP image data and displays an ultrasound image.
Moreover, in this conventional art, after the MIP process is executed in a direction to the endocardium, data is projected to a two-dimensional plane and the projected data is displayed.
Diagnosis of myocardial ischemia requires grasp of how ischemic portions of the myocardium are distributed from the inside to outside of the myocardium. However, it is difficult for an observer to grasp how the ischemic portions are distributed based on an ultrasound image generated by the ultrasound imaging apparatus of the conventional art. Even if, for example, an MIP image or a three-dimensional image generated by volume rendering is displayed, it is difficult for the observer to clearly grasp the distribution of the ischemic portions.
Further, since the MIP image is an image obtained by projecting volume data to a two-dimensional plane, it is hard to three-dimensionally see.
Although the MIP image is displayed while the volume data is rotated in the conventional art, it is difficult for the observer to grasp how the ischemic portions are distributed from the inside to outside of the myocardium.
Further, a three-dimensional image generated by volume rendering is generally subjected to the shadowing process so as to three-dimensionally show a subject represented in the image. Because of this shadowing process, the three-dimensional image does not clearly show shading represented in the original data, and therefore, it is difficult for the observer to read the shading from the three-dimensional image. Accordingly, it is difficult to grasp the distribution of the ischemic portions in the myocardium only by the three-dimensional image generated by volume rendering.
Thus, it is required to display so that the operator can easily grasp distribution of lesion sites, such as the distribution of the ischemic portions in the myocardium.